1. Field of the Invention
This invention relates to a signal processing system for monitoring the arcing potential of generator brushes and more particularly to circuitry for monitoring a generator brush arcing potential which is included in a composite signal further including recurring noise spikes which are in the same frequency band as the brush arcing potential.
2. Description of the Prior Art
U.S. Pat. No. 3,653,019, which was issued to the assignee of the present application on an invention of one of the co-inventors of the present system, discloses a system for monitoring brush arcing potential in a generator where the excitation voltage supplied to the brushes contains high energy noise spikes in the same frequency band as the brush arcing potential. The system disclosed in that patent was designed to enable detection of excessive arcing and prevent damage to brush holder riggings and deterioration of collector slip rings. If action to remedy the excessive arcing is not taken promptly severe damage can occur resulting in considerable downtime for repair of equipment. Use of the signal monitoring system disclosed in that patent not only reduces such downtime, but also provides means to determine when brush condition begins to deteriorate so the equipment may be taken out of service for brush replacement at convenient times. Without a means of detection of such a trend of deterioration sudden failure of equipment might require repair during peak power demand periods when such equipment outage is least desirable.
The signal monitoring system disclosed in U.S. Pat. No. 3,653,019 has proven very effective in performing the function for which it was designed, but it lacks some versatility making it difficult or even impossible to use the system with some generators. In particular, the system does not have the capability of monitoring low potential brush arcing, although low potential, high currents arcing on some generators has been found to be destructive. Also, optimum performance of the system is dependent upon a regularity of recurrence of noise spikes, with increases in the time interval between successive noise spikes causing a decrease in the probability of detecting destructive arcing. This decrease in probability occurs since a gating network employed in the system passes received signals only for a predetermined time period following each noise spike. Therefore, as the time interval between spikes increases the percentage of time that the gating network passes signals decreases and so does the likelihood of detecting destructive arcing.
The present signal monitoring system overcomes these difficulties. It is usable for monitoring of brush arcing in a wide range of generators, from those having very low destructive arcing potentials to those having arcing potentials of the higher amplitudes monitored by the older system. Also, there is substantial certainty of detecting destructive arcing regardless of the existence or lack of noise spikes and regardless of increases in the time interval between successive noise spikes. Such an improvement in the probability of detection occurs since the gating network of the present system passes received signals at all times rather than during a predetermined time period coincident with the actual occurrence of a noise spike. In addition, the present system has fewer components, resulting in improved reliability.